It is an important issue for the entire society to reduce the electric power consumption of electronic devices, illumination devices, and the like and to promote the usage of renewable energy. In order to reduce the electric power consumption, for example, a display of an electronic device and an illumination device use photoelectric conversion elements consuming less electric power such as a light-emitting diode (LED).
On the other hand, in particular, portable devices such as a smartphone and a tablet terminal do not necessarily have sufficient battery capacity for their electric power consumptions, and this results in frequent battery charge, which makes it difficult for everyday use. For this reason, there is an attempt to additionally provide a solar battery to the portable device. By using the solar battery, use of renewable energy in the portable device is promoted.